1. Field of the Invention
The invention relates to shaft bearings, and in particular to a bearing for the lower end of a rotatable, vertically suspended shaft, wherein the bearing includes means to not only compensate for angular misalignment, but also to accommodate off-center alignment of the shaft relative to the centerline of a vessel in which the shaft is housed.
2. Description of the Prior Art
For many years the chemical industry has used elongate, vertical, processing vessels of the type having elongate, rotatable impeller shafts which extend throughout the entire length of the vessels. The impeller shafts are rotatably suspended and driven from the top or upper end of the vessels, and since the height of the vessels are often fifty feet or more, with a diameter of seven or more feet, the technique of providing a long lasting bearing support for the lower end of the impeller shafts has left much to be desired, and has presented a serious problem for the industry.
Heretofore it has been the practice to lower an impeller shaft into a vessel in order that a workman, who has entered the bottom of the vessel beneath the lower end of the shaft via a porthole in the side of the vessel, will have access to the lower end of the shaft in order to fit a bearing onto the lower end thereof. A tripod bearing support was associated with the bearing, after which the shaft was hand rotated in order that the workman could observe the path described by the shaft end relative to the centerline of the vessel, after which he would mark that position of the bearing which would provide the least amount of shaft distortion incident to rotation thereof. The legs of the tripod bearing support were then tacked to the inner surface of the bottom head of the vessel, after which the shaft would be lifted to disengage the bearing until the legs of the bearing support were securely anchored in place, by means of welding. The shaft was then lowered for disposing its lower end in the bearing.
By reason of the long length of impeller shafts it is and was difficult, if not impossible, to rotatably suspend them from their upper ends in such a manner as to locate them in parallelism with the center line of their vessels, with the result that angular misalignment of shafts relative to the centerline of their respective vessels was inevitable. Any such angular misalignment results in the lower end of the shaft being rotated off-center with respect to the centerline of a vessel, which produces a situation in which such excessive wear occurs on the bottom bearings, as to shorten their useful life to a period of from three to six weeks.
Whenever it became desirable or necessary for the bottom bearing to be inspected or replaced, the vessel would be emptied, and if the contents thereof were toxic or otherwise harmful, sticky or dangerous, the interior of the vessel would be purged, after which a workman would enter the bottom of the vessel via a side manhole to obtain access to the bearing. If the bearing required replacement, the shaft would be raised, the old bearing removed from the tripod support and replaced with a new bearing, after which the shaft end was guided into the new bearing by the workman who would then crawl out of the manhole, which when closed permitted the vessel to be recharged and again put in operation.
In certain instances access to the bottom bearings was possible only by lowering a workman into a vessel, after the impeller shaft was completely withdrawn in order that the bearing could be inspected and/or replaced.
I am aware of the use of double eccentrics as means for adjusting the center line of a shaft relative to a bearing support in those instances in which there is axial alignment of a shaft with respect to the bearing; however, the more use of double eccentrics as a means for accommodating displacement of the lower end of an impeller shaft with respect to the centerline of a vessel will not solve the problem created by angular misalignment of the shaft relative to the said centerline.
I am aware of the following patents which disclose the use of double eccentrics for the purpose of adjusting the center line of the shaft relative to a support member viz: U.S. Pat. Nos. 1,571,557 to W. L. Paul; 2,711,935 to W. H. Miles; 2,826,462 to L. B. Evans; 2,860,015 to P. D. Matterson; 2,920,497 to R. Wilken; 3,453,031 to S. S. Rickley et al; and 3,467,450 to H. K. Schmidt et al.